1. Field of the Invention
The present is directed generally to a soldering apparatus having at least one stirrup electrode and more, particularly, to a soldering apparatus for placing a rectangular work surface of a stirrup electrode onto a soldering location.
2. Description of the Related Art
A soldering apparatus is disclosed, for example, in German published application 31 49 236. In this known soldering apparatus, an electrode holder includes small columns of conductive material electrically insulated from one another between whose ends at least two stirrup electrodes are secured in interchangeable fashion. The U-shaped stirrup electrodes that can be heated by electrical resistance heating are made of a planar plate of resistor material, such as tantalum or molybdenum, and are attached in such fashion that their working surfaces lying at their underside to come into contact with elements to be soldered. Given two stirrup electrodes lying opposite one another, or four stirrup electrodes lying opposite one another in pairs, a total of four small columns are required for the electrode holders. The columns are arranged in a respective diagonal of the cross-section of the soldering apparatus and are mechanically connected to one another by a plurality of cross-shaped bracings. For the power supply of the four stirrup electrodes, two small columns lying on a diagonal are connected to one pole of a power source, while the two other small columns are connected to the other pole of the power source.
A soldering apparatus having two stirrup electrodes lying parallel and opposite to one another, or having four stirrup electrodes lying opposite to one another in pairs, is particularly utilized for soldering electronic components, such as multiple micropacks, flatpacks and the like, to printed circuit boards. The resistance heating of the stirrup electrodes is caused by current pulses which pass therethrough.
Reliable contact between the working surfaces of the stirrup electrodes, the terminal legs of the components, and the interconnects or terminal pads of the printed circuit boards must be guaranteed both before the soldering process as well as over the entire duration of the soldering process. This requirement, however, cannot be always be met in view of the possible electrical arcing which occurs on the printed circuit boards, the tolerance variations of the printed circuit boards in a direction perpendicular to the plane of the circuit board, the tolerance variations in layer thicknesses, and the possible skewed positioning of the printed circuit boards during the soldering process.